The present invention relates to a gelating agent for an alkaline cell and an alkaline cell. More particularly, the present invention relates to a gelating agent of a gel type anode for an alkaline cell comprising the anode containing an alkaline electrolytic solution and a zinc powder as a mainly component and using the gelating agent and also to an alkaline cell using the gelating agent.
Conventionally, mainly used for an anode of an alkaline cell is a mixture containing an alkaline electrolytic solution in a high concentration (an aqueous high concentration potassium hydroxide solution, if necessary, containing zinc oxide) and a zinc powder and/or a zinc alloy powder and for the purpose of preventing the precipitation of the zinc powder in the alkaline electrolytic solution, an anode proposed as the gelating agent are water-absorptive resin materials with relatively large particle size and comprising poly(meth)acrylic acids and their salts made insoluble by cross-linking agents [(i) Japanese Patent No. 8-28216, (ii) Japanese Patent No. 8-12775, (iii) Japanese Patent Laid-Open No. 10-50303, and the like).
However, these gelating agents are not necessarily satisfactory in prevention of precipitation of a zinc powder, liquid leakage from a cell, and drain of gelating agents, in productivity of cells, and the like.
Inventors of the present invention have enthusiastically made investigations taking the above described situation into consideration and surprisingly found that gelating agents whose stringiness, particle size and the like are defined within specified ranges have improved properties in the above described disadvantages and provide remarkably desirable results in the discharging property, the life, the impact resistance, the workability, and the like of a cell and thus achieved the present invention.
A first purpose of the present invention is to provide a gelating agent providing remarkably excellent effects on sustainability of electric discharge and impact resistance of an alkaline cell.
A second purpose of the present invention is to provide a gelating agent of an alkaline cell capable of providing an excellent property in stringiness of an alkaline electrolytic solution and dealing with the high speed packing of the alkaline electrolytic solution.
A third purpose of the present invention is to provide a gelating agent of an alkaline cell effective to manufacture a cell with uniform quality with little unevenness in the packed amount of an electrolytic solution even in the case of mass production.
A fourth purpose of the present invention is to provide a gelating agent of an alkaline cell capable of preventing hydrogen gas evolution even if it is brought into contact with a zinc powder in an electrolytic solution and having no probability of causing leakage of an electrolytic solution and damaging a cell attributed to the inner pressure of the cell.
A fifth purpose of the present invention is to provide an alkaline cell using such a gelating agent.
In other words, the present invention provides the following gelating agents [1] to [14] and an alkaline cell [15].
[1] Gelating Agent:
A swelling-in-water type gelating agent of a cross-linked polymer (A) comprising (meth)acrylic acid and/or its alkali metal salt as a main constituent monomer unit and obtained by an aqueous solution polymerization or a reversed phase suspension polymerization, wherein the gelating agent for an alkaline cell satisfies the following required conditions (1), (2):
required condition (1); that the gelating agent contains 50% by weight or more of a particle whose swollen particle size becomes 300 to 4,000 xcexcm when the gelating agent is swollen in an aqueous potassium hydroxide solution of 40% by weight concentration; and
required condition (2); that the aqueous potassium hydroxide solution of 40% by weight concentration containing 3% by weight of the gelating agent has 0 to 20 mm stringiness.
[2] Gelating Agent:
A gelating agent for an alkaline cell satisfies the required condition (3) in addition to the foregoing conditions (1), (2):
required condition (3); that the aqueous potassium hydroxide solution of 40% by weight concentration containing 3% by weight of the gelating agent has viscosity of 50 to 1,000 Pa.s at 40xc2x0 C. after one day and sixty days.
[3] Gelating Agent:
A gelating agent for an alkaline cell satisfies the required condition (4) in addition to the foregoing conditions (1), (2) or (1) to (3):
required condition (4); that the gelating agent contains 0 to 15 ppm of a metal with a lower ionization tendency than zinc.
[4] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [1] containing the swollen particle satisfying the foregoing required condition (1) whose particle size is 500 to 2,000 xcexcm.
[5] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [1] containing 0 to 30% by weight of soluble components in an aqueous potassium hydroxide solution of 10% by weight concentration when the gelating agent is swollen in the said aqueous solution.
[6] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [1], wherein the forgoing polymer (A) is a cross-linked polymer with 5,000 to 1,000,000 average polymerization degree and cross-linked by an allyl ether type cross-linking agent (b) having 2 to 10 of allyl groups in a molecule and added in 0.05 to 1.0% by weight to the total weight of the (meth)acrylic acid and/or its alkali metal salt.
[7] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [6], wherein the forgoing agent (b) has 3 to 10 of allyl groups in a molecule and 1 to 5 of hydroxyl groups in a molecule.
[8] a Gelating Agent:
A swelling-in-water type gelating agent of a cross-linked polymer (Axe2x80x2) obtained by cross-linking a polymer which comprises (meth)acrylic acid and/or its alkali metal salt as a main constituent monomer unit, has 5,000 to 1,000,000 average polymerization degree and is produced by an aqueous solution polymerization or a reversed phase suspension polymerization, with an allyl ether type cross-linking agent (b) having 2 to 10 of allyl groups in a molecule and added in 0.05 to 1.0% by weight to the total weight of the (meth)acrylic acid and/or its alkali metal salt, wherein the gelating agent for an alkaline cell satisfies the following required conditions (1) to (4): required condition (1); that the gelating agent contains 50% by weight or more of a particle whose swollen particle size becomes 300 to 4,000 xcexcm when the gelating agent is swollen in an aqueous potassium hydroxide solution of 40% by weight concentration; required condition (2); that the aqueous potassium hydroxide solution of 40% by weight concentration containing 3% by weight of the gelating agent has 0 to 20 mm stringiness; required condition (3); that the aqueous potassium hydroxide solution of 40% by weight concentration containing 3% by weight of the gelating agent has viscosity of 50 to 2,000 Pa.s at 40xc2x0 C. after one day and sixty days; and required condition (4); that the gelating agent contains 0 to 15 ppm of a metal with a lower ionization tendency than zinc.
[9] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [1], wherein the polymer (A) is obtained by polymerizing a monomer comprising mainly (meth)acrylic acid and/or its alkali metal salt with neutralization degree of 0 to 30% by mole and neutralizing the polymer based on necessity after polymerization.
[10] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [1] obtained by carrying out permeation drying and/or ventilation drying based on necessity after segmentation of water-containing gel in the process of drying the water-containing gel of the polymer (A) or carrying out vacuum drying and/or ventilation drying after solid-liquid separation of the water-containing gel.
[11] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [8] containing the swollen particle satisfying the foregoing required condition (1) whose particle size is 500 to 2,000 xcexcm.
[12] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [8] containing 0 to 30% by weight of soluble components in an aqueous potassium hydroxide solution of 10% by weight concentration when the gelating agent is swollen in the said aqueous solution.
[13] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [8], wherein the polymer (Axe2x80x2) is obtained by polymerizing a monomer comprising mainly (meth)acrylic acid and/or its alkali metal salt with neutralization degree of 0 to 30% by mole and neutralizing the polymer based on necessity after polymerization.
[14] Gelating Agent:
A gelating agent for an alkaline cell is the gelating agent as defined in [8] obtained by carrying out permeation drying and/or ventilation drying based on necessity after segmentation of water-containing gel in the process of drying the water-containing gel of the polymer (Axe2x80x2) or carrying out vacuum drying and/or ventilation drying after solid-liquid separation of the water-containing gel.
[15] Alkaline Cell:
An alkaline cell using a gelating agent of [1] to [14].